1. Field of the Invention
This invention relates to a method for preventing a plate type heat exchanger from blockage, and more particularly to a method for preventing a plate type heat exchanger used in an apparatus for disposal of discharge gas from blockage.
2. Description of the Related Art
The heat exchanger for effecting transfer of heat between two fluids, one having a high temperature and the other a low temperature is one of the chemical machines which are used copiously in the chemical industry. The principle of the heat exchanger resides in exchange of heat between a fluid of a high temperature and a fluid of a low temperature through the heating surface.
Generally, the heat exchanger effects the exchange of heat by introducing a fluid aimed at exchanging heat and by cooling or heating into a heat exchange part in the apparatus. The heat exchange part is known that there are various types such as the shell-and-tube type which has a multiplicity of tubes bundled and inserted in a shell; the plate type which has heat transfer plates forming corrugated ribs or hemispheric ridges therein superposed and clamped through the medium of such gaskets as used in a filter press and also has thin flow paths of a rectangular cross section each interposed between the adjacent plates and which effects exchange of heat between a fluid of high temperature and a fluid of low temperature by causing these fluids to flow through these flow paths on alternating levels; and the fin tube type which has heat transfer tubes provided on the inner and outer surfaces thereof with fins thereby enabling the heat transfer tubes to acquire an increased heat transfer area with a view to exalting the efficiency of heat transfer.
These heat exchangers are sorted by nature of use into (1) a heater which is a heat exchanger to be used for the purpose of heating a fluid to a required temperature without inducing the fluid to undergo phase change, (2) a preheater which is a heat exchanger to be used for the purpose of heating a fluid in advance and enhancing the efficiency of the subsequent operation to be performed thereon, (3) a superheater which is a heat exchanger to be used for the purpose of heating a fluid till a superheated state, (4) a vaporizer which is a heat exchanger to be used for the purpose of vaporizing a fluid by application of heat, (5) a reboiler which is a heat exchanger to be used for the purpose of heating again a fluid which has been condensed in a device thereby vaporizing the fluid, (6) a refrigerator which is a heat exchanger to be used for the purpose of cooling a fluid till a required temperature, (7) a chiller which is a heat exchanger to be used for cooling a given object to a very low temperature of not more than 0° C., (8) a condenser which is a heat exchanger to be used for the purpose of cooling a condensing gas till liquefaction by condensation, (9) a total condenser which is a heat exchanger to be used for the purpose of wholly condensing a condensing gas, and (10) a partial condenser which is a heat exchanger to be used for the purpose of liquefying part of a condensing gas by condensation and releasing the remainder of the gas in the form of gas. They are copiously used in these applications.
One example of the heat exchange to be effected by the use of the plate type heat exchanger will be described below with reference to FIG. 1. It is provided, however, that the outlets and the inlets for the heat exchanging gas and/or other gas which will be described herein below may be reversed, depending on purpose or necessity. In addition, the direction of installation of the heat exchanger does not need to be limited to verticality but may be selected, depending on the kind of gas or fluid to be handled and the purpose of use of heat exchanger.
For a start, with reference to FIG. 1, 10 denotes a shell, 11 a gas outlet, 12 a gas inlet, 22 a heat-exchanging gas introduction port, 23 a heat-exchanging gas discharge port, and 30 a heat exchange part.
In this heat exchanger, the gas which is aimed at exchanging heat is supplied through the heat-exchanging gas introduction port 22, then introduced into the heat exchange part 30, and discharged through the heat-exchanging gas discharge port 23. The other gas for exchanging heat with the heat-exchanging gas is introduced into the shell 10 through the gas inlet 11, then caused to exchange heat with the heat-exchanging gas efficiently in the heat exchange part 30 and while alter the flow path thereof, and guided out of the gas outlet.
The gas processing device such as the plate type heat exchanger under discussion is generally used, while carrying out the processing, as a heater and/or a cooler for the purpose of retaining the required temperature or recovering the heat. When the heat-exchanging gas happens to contain an easily blocking substance, it often gives rise to blockage between the adjacent plates. Since this blockage stops the device, the blocking substance must be removed artificially or chemically. When the device is intended for continuous mass production as in the production of a general-purpose chemical substance, the stop of the device forms the cause for lowering the efficiency of production. The method for installing two identical gas processing devices and putting them to use alternately may be conceived for the purpose of avoiding the trouble mentioned above. This method, however, proves unduly expensive.
Further, the plate type heat exchanger generally has a smaller cross-sectional area in the gas introduction port than in the heat exchange part. If the cross-sectional area in the gas introduction port is equalized with that in the inlet part of the heat exchange part, the gas pipes will have to be enlarged and the cost of equipment will be consequently heightened. When the cross-sectional area in the gas introduction port and that in the heat exchange part are different, this difference forms a cause for lowering the ratio of heat exchange because the heat-exchanging gas is supplied in an increased amount to the central part of the heat exchanger and the gas is supplied in a decreased amount to the peripheral part of the heat exchanger. No contrivance whatever for uniformizing the supply of gas, however, has been made for the heat exchange part destined to introduce the heat-exchanging gas.
Particularly when the heat-exchanging gas contains an easily blocking substance, an uneven ratio of heat exchange results in local generation of a blocking substance due to adhesion or accumulation of the easily blocking substance. Absolutely no countermeasure has ever been made with respect to this blockage. When the gas containing the easily blocking substance is the discharge gas generated during the process for producing acrylic acid, for example, this gas often contains easily blocking acrylic acid. When this gas is heat exchanged and then subjected to oxidizing decomposition and discarded, therefore, the intervals between the adjacent plates form blockage with the acrylic acid and other easily blocking substances contained during the heat exchange. When the gas containing the easily blocking substances is subjected to heat exchange as described above, the uneven supply of the gas degrades the thermal efficiency and the concentration of the feed gas results in generating the blocking substance in part of the heat exchange part and consequently compelling the entire device to stop its operation. The use of this gas brings such problems as inducing adhesion of the blocking substance to the heating surface and consequently degrading the efficiency of heat transfer. All these disadvantages still remain yet to be solved.